BEIRUT (AP) -- Syrian government forces and allied militias captured Aleppo's centrally located al-Shaar neighborhood from rebels on Tuesday, securing nearly three quarters of the besieged enclave less than two weeks after launching a ground offensive, according to the Syrian military.

The Syrian government and its ally Russia meanwhile rejected a cease-fire for the war-torn city, keeping up the military offensive amid rebel retreats and massive displacement.

Rebels withdrew from al-Shaar under heavy bombardment by pro-government forces to the Marjeh and Maadi neighborhoods, local media activist Mahmoud Raslan told The Associated Press. Several gunmen were killed.

"Morale has hit rock bottom," he said from inside the city's remaining rebel-held enclave.

The SANA state news agency said the government captured the entire neighborhood as well as the neighborhoods of al-Qatarji and Karm al-Dada.

A map provided by the Syria army showed a quickly shrinking opposition enclave- a pointed leaf-shaped territory in the center, abutting already government-controlled Aleppo districts. The army media said the new gains bring the area controlled by the government in eastern Aleppo to about 73 percent of its original size, which is estimated to be about 45 square kilometers (17 square miles.)

The Britain-based Syrian Observatory for Human Rights monitoring group also reported the gains.

Al-Shaar was home to at least four hospitals available to residents trapped by the government's siege of the eastern part of the city. But those hospitals, along the rest of the neighborhood, were bombed by the government's attacks and evacuated. Broad swaths of the city's eastern quarters are in ruins.

Ibrahim al-Haj, a civil defense member, said he was in the neighborhood shortly before it fell to the government. "It is totally destroyed," he said, adding that if he had stayed a minute longer he would have been captured. He said the previously densely populated district had largely been deserted since the government forces first moved in on the eastern districts last weekend.

A government intense aerial offensive had preceded the ground troops' advances.

Rebel defenses are collapsing under the weight of twin offensives by pro-government forces.

Rebels and pro-government forces fought street-to-street in the city's southern Saif al-Dawleh and al-Zabadiyeh neighborhoods, according to footage provided by Syrian military media and audio provided by local teacher and media activist Abdelkafi Alhamdo.

The Syrian government and its ally Russia on Tuesday issued stark warnings to rebels in besieged eastern neighborhoods of Aleppo, with Moscow's top diplomat saying the rebels will be wiped out unless they stop fighting and leave the city.

Damascus also said it rejects any cease-fire for Aleppo that does not include the departure of all rebels from the eastern part of the city and that it won't allow the rebels to use a truce as a chance to "regroup."

The tough rhetoric comes a day after Russia and China blocked a draft resolution at the U.N. Security Council demanding a seven-day truce in Aleppo to evacuate the sick and wounded and to provide humanitarian aid workers time to get food and medicine into the city. Russia, a main backer of the Syrian government, is supporting the government's offensive in Aleppo and has repeatedly blocked action in the Security Council over Syria.

"Those who refuse to leave nicely will be destroyed," Russian Foreign Minister Sergey Lavrov told reporters in Moscow, speaking of the Syrian rebels. "There is no other way."

In Damascus, the Foreign Ministry said in a statement carried on the state SANA news agency, that the government will not allow rebels a chance to "regroup and repeat their crimes" in the divided city - a reference to rebel shelling of Aleppo's western, government-held districts that has killed 81 civilians in the past three weeks, according to the Observatory.

The government's offensive to take eastern Aleppo killed 341 civilians over the same period and displaced tens of thousands over the past week, the Observatory and other activist groups have said.

Residents in the city's east reported heavy shelling and bombardment overnight.

"A rocket struck the fifth floor of the building we are staying in, but thankfully no one was hurt," said Judy al-Halaby, an activist sheltering in the Mashhad neighborhood.

Meanwhile, rebel shelling of of Foua and Kfarya, two besieged pro-government towns in northwestern Idlib province killed at least 10 people, many from the same family, according to a Facebook page operated by activists in the predominantly Shiite towns. The Observatory put the death toll in the two towns at 12, including three children.

At the press conference in Moscow, Lavrov lamented what he described as attempts by the United States to obtain a pause in the fighting in Aleppo to allow rebels to re-arm and re-supply. He said that "serious conversations with our American partners are not working."

U.S. Secretary of State John Kerry said Tuesday that he hopes to convince Syria's warring factions and their backers to return to the negotiating table before Aleppo is destroyed.

Kerry said he is due to meet Lavrov in Hamburg, Germany on Thursday and would try to find a way forward.

Earlier, Russian President Vladimir Putin's spokesman said the Kremlin regrets a "more than modest" reaction by the international community following a rocket attack on a Russian military hospital in Aleppo on Monday that killed two Russian nurses.

Russian officials alleged rebels were provided coordinates to the hospital by a foreign power, though they did not specify a particular country.

After the Russian and Chinese veto at the Security Council, U.S. diplomats accused their Russian counterparts of stalling for time as Syrian government forces advance in Aleppo.